Capricorn Posted April 18, 2011 Share Can I throw my hat into the "hydraulic fluid heats up too much" ring? How hot do these brakes get? How hot do the brakes on my motorbike get? Can we get something behind all this? I use dot 4 race on the motorbike, can I use that on the mtb? It will destroy seals, wont it? I have to use mineral oil, don't I? I think the marketers saw you lot coming a mile off. i dont drag my brakes, but after one run, i accidentaly had my calf touch the rear disc: hair singed, skin blistered. how hot u reckon that is? funnily enough it's mostly the fun riders that test the heat limits of brakes... Edited April 18, 2011 by Jarek Wysocki Link to comment Share on other sites More sharing options...
brad890 Posted April 18, 2011 Share Can I throw my hat into the "hydraulic fluid heats up too much" ring? How hot do these brakes get? How hot do the brakes on my motorbike get? Can we get something behind all this? I use dot 4 race on the motorbike, can I use that on the mtb? It will destroy seals, wont it? I have to use mineral oil, don't I? I think the marketers saw you lot coming a mile off. well from what i've experienced the rotors get pretty hot, have a nice long steep hill i like to train on, and when i come back down and sit on the breaks, have to as hitting switchback at 40-60km plus wouldnt work so well lol. the rotors get flipping hot, dripping water on them from the camelback causes the water to instantly turn to steam, like dripping water onto a hot frying pan lol. Link to comment Share on other sites More sharing options...
TNT1 Posted April 18, 2011 Share I'm just saying, on the m/bike, I can almost guarantee (need an experts weigh in) that the pads/discs/oil get hotter, and I don't get fade, and glazing, and seals dying, and so on. And I only use sintered pads, rain/mud or shine/dry-like-a-desert... I still maintain, that science aside, the bicycle industry of late is a marketers' money making racket. Link to comment Share on other sites More sharing options...
TNT1 Posted April 18, 2011 Share well from what i've experienced the rotors get pretty hot, have a nice long steep hill i like to train on, and when i come back down and sit on the breaks, have to as hitting switchback at 40-60km plus wouldnt work so well lol. the rotors get flipping hot, dripping water on them from the camelback causes the water to instantly turn to steam, like dripping water onto a hot frying pan lol. Come round tomorrow, and squirt some juice on my motard's discs and pads when I've just ridden home from work. Link to comment Share on other sites More sharing options...
NotSoBigBen Posted April 18, 2011 Share I still maintain, that science aside, the bicycle industry of late is a marketers' money making racket. And then they back that up with crap service at the agent and the bike shop ...... Link to comment Share on other sites More sharing options...
TNT1 Posted April 18, 2011 Share And then they back that up with crap service at the agent and the bike shop ...... Dammit, and then the race entry fees. It's madness. Link to comment Share on other sites More sharing options...
Johan Bornman Posted April 18, 2011 Share it's not the pads, but the friction-induced heat caused from prolonged braking. The heat transfers to the hydraulic fluid (if u have hydraulic brakes) and causes air bubbles to form. Air bubbles are much more compressible than the hydraulic fluid, and causes your brakes to feel 'spongy' that is to say, it will lack proper feedback between pulling on the lever and the expected braking effect... Uhmmm...how does heat generate air? Link to comment Share on other sites More sharing options...
brad890 Posted April 18, 2011 Share Uhmmm...how does heat generate air? well the only way i think that air could be a factor, is if the brakes weren't bled properly and the heat could possible cause the gas in the bubble (already there before) to expand, other then that to convert the brake fluid from its liquid form to a gas form would take quite allot of energy/heat i guess? come on Johan i know you want to give us the nice technical reason that one experiences brake fade? lol Edited April 18, 2011 by brad890 Link to comment Share on other sites More sharing options...
Johan Bornman Posted April 18, 2011 Share well the only way i think that air could be a factor, is if the brakes weren't bled properly and the heat could possible cause the gas in the bubble (already there before) to expand, other then that to convert the brake fluid from its liquid form to a gas form would take quite allot of energy/heat i guess? come on Johan i know you want to give us the nice technical reason that one experiences brake fade? lol Aaag nee man. Dink 'n bietjie! Look inside your kettle whilst it is working. Soon you'll see bubbles forming around the element and eventually, big bubbles rising to the surface. What gas is in those bubbles? Link to comment Share on other sites More sharing options...
Moolz Posted April 18, 2011 Share So the question... To go sintered or not go to sintered?I have had resin pads - and they are great (considering that I have no sintered experience)...Recently my rides have been wet and muddy - and i still have tons of pad left (ive done 850km so far)...To note: im pretty heavy on brakes... How much of a difference will i feel with sintered?Running a super entry level M486 Shimano - XT 180mm rotor up front and a resin-only 160mm in the rear...What would happen if I used a sintered on the rear rotor? Link to comment Share on other sites More sharing options...
brad890 Posted April 18, 2011 Share Aaag nee man. Dink 'n bietjie! Look inside your kettle whilst it is working. Soon you'll see bubbles forming around the element and eventually, big bubbles rising to the surface. What gas is in those bubbles? ok ok i'm not a physicist lol.. here is the wiki extract i found "The reduction of friction termed brake fade is caused when the temperature reaches the "kneepoint" on the temperature-friction curve. [All brake lining is cured under mechanical pressure following a heating & cooling curve, heating the friction material up to 450°F to "cure" (cross-link) the phenolic resin thermoset polymers: There is no melting of the binding resins, because phenolic resins are thermoset, not thermoplastic] In this form of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels "spongy". This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance." http://en.wikipedia.org/wiki/Brake_fade Link to comment Share on other sites More sharing options...
Johan Bornman Posted April 19, 2011 Share ok ok i'm not a physicist lol.. here is the wiki extract i found "The reduction of friction termed brake fade is caused when the temperature reaches the "kneepoint" on the temperature-friction curve. [All brake lining is cured under mechanical pressure following a heating & cooling curve, heating the friction material up to 450°F to "cure" (cross-link) the phenolic resin thermoset polymers: There is no melting of the binding resins, because phenolic resins are thermoset, not thermoplastic] In this form of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels "spongy". This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance." http://en.wikipedia.org/wiki/Brake_fade Wiki is good. I wish more people would research some fundemental stuff there. I was originally asking the other oke how heat in the system magically generates air from an environment where there is no air. I thought that maybe he has solved the dilemma of manufacturing air from nothing. I was just fooling around.The bubbles generated around a kettle's element and for that matter, inside a braking system, are not air but vaporised fluid of whatever kind was in the system. In the kettle, it is water vapour, in the brake system, it is brake fluid vapour or, if the system was contaminated, water vapour. We get different types of brake fade. 1) Fluid fade. This is when the fluid in the system boils, creating compressible bubbles. The symptoms are (ask Kevin), a lever that at the beginning of of the descent, felt hard but under hard braking became softer and softer until it eventually bottoms out against the bar. If you survive the incident, you may be puzzled afterwards, because the brake will work perfectly again. 2) Green fade. This only happens with new pads. Pads are made from various things bound together by a form of glue (resin). This resin is like epoxy glue. Even when it is hard, it is not yet fully cured and by heating it, it cures a bit more. Unfortunately it gives of gas in this final cure. This gas escapes from the pad as you brake and forms a gas lubricant which prevents you from stopping. It sits betweeen the pad and disc like a cushion. Green fade is the rason why pad manufacturers ask you to break the brakes in first, but applying 20 or 30 gentle stops. If you don't do this, one big braking event could see you fall thanks to green fade. Alternatively, before the pads are completely outgassed, they can still melt and then glaze the discs, which kinda ruins them forever. 3) Pad fade. Various friction materials perform better (i.e. have more friction) at different temperatures. Some work better when cold, other better when very hot. Pad fade is when you exceed the material's intended temperature and it starts to melt. Sintered metal can melt too. Resin pads technically don't melt (they sublimate, which is skipping the molten state and going directly to smoke) but this process still gives you brake fade. Sintered metal vs organic pads, vs resin pads. In bicycles, most of the sintered metal pads are actually combination of resin an bits of metal and, organic pads also have some resin in. The common demoninator is resin and most pads thus suffer from the bad effects of resin. Sintered metal is just some metal filings or fine metal wire that was heated to just below the metal's melting point and then crushed into shape under high pressure. Metal pads are made from brass and copper and perhaps zinc - all metals softer than steel. A bit of resin may bind them or they can be pure sintered, containing no resin. I doubt that's the case in bicycle brakes but I stand to be corrected. Sintered pads These pads last a long time but are quite aggressive to the disc. They can work at high temperatures but, require more lever pressure to operate. Some discs may not be made from metal tough enough to work with syntered metal pads and thus have a warning on them. Resin pads. Sometimes called organic pads, these are made of fibres - asbestos (now illegal), kevlar, cellulose and other secret stuff - that's all held together with resin. These pads are kind to the discs, require very little effort to brake and smell like Satan's bottom when overheated. When they overheat, they mess kup the disc by coating it in hardened goo. They don't like working in the wet since they just abrade away within a couple of stops, given gritty wet conditions. This is not a pure definition, since most pads are a combination of the above two types. In cars, fancy stuff like ceramic and carbon dust is also added to the pads but that's not for here. Since my pads are still rubber, I don't have much experience with how the different types perform in the field, perhaps the other posters here can give us their experience. Link to comment Share on other sites More sharing options...
dirtrider Posted April 19, 2011 Share You asked for it !! Like you have so rightly mentioned , the organic/resin pads takes a lot less effort to bring you from 60 to 0 in the shortest distance but they wear very quickly . Not my pad of choice . The Metal pads takes more effort to get you standing still , can be VERY noisy especially when wet and I assume generated a lot of heat (well more that organics , but this is just an assumption) . But why drag you brakes to start off with ? If you have the need to go down a steep hill slowly then surely you should alternate braking between front and back giving them time to get a bit of cool air ? And should the brakes be used for when you want to stop ? You spend a lot of effort and maybe a hour or two to get to the top , to test your brakes going down the other side ? Link to comment Share on other sites More sharing options...
Capricorn Posted April 19, 2011 Share talking in simple terms so as not to confuse the issue. the exact physical detail is not necessary JB. But feel free to be the physicspolice.. carry on then.. Link to comment Share on other sites More sharing options...
The Drongo Posted April 19, 2011 Share After a race this weekend my front and rear pads of my HOPE TECH X2 brakes needs to be replaced. I found some on buycycle, but it's the sintered version. Hope says that the sintered version is not recommended for dry conditions. On crc i can get sintered or organic. Whats the difference? So picaso, is your question answered? Link to comment Share on other sites More sharing options...
The Drongo Posted April 19, 2011 Share it's not the pads, but the friction-induced heat caused from prolonged braking. The heat transfers to the hydraulic fluid (if u have hydraulic brakes) and causes air bubbles to form. Air bubbles are much more compressible than the hydraulic fluid, and causes your brakes to feel 'spongy' that is to say, it will lack proper feedback between pulling on the lever and the expected braking effect... Fixed. THE SIMPLE ANSWER. Link to comment Share on other sites More sharing options...
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